1. Field of the Invention
The present invention relates to an image reading apparatus capable of processing paper fingerprint information, a method for the image reading apparatus, and a storage medium storing a program realizing the image reading method.
2. Description of the Related Art
Internet-based digital technologies enable users to easily acquire various types of information. In this respect, to prevent leakage of information, reliable security technologies for information processing devices are recently required.
Some security technologies can guarantee authenticity of a document sheet or a print sheet used in an image processing apparatus, such as a copying machine or a multifunction peripheral (MFP). For example, a conventional security technology uses paper fingerprint information because paper includes numerous plant fibers having a size of 20 to 30 microns. Plant fibers, in an entangled state, form a random pattern, which can be generally referred to as “paper fingerprint information.” Like a fingerprint, paper fingerprint information is unique to each sheet. An example method for guaranteeing the authenticity includes acquiring (registering) paper fingerprint information and performing collation.
A reading apparatus including an optical unit can perform registration and collation of paper fingerprint information. To acquire paper fingerprint information, the reading apparatus detects a shade pattern of plant fibers in a white area of paper. To this end, the optical unit reduces the quantity of light emitted toward a document when the reading apparatus reads paper fingerprint information, compared to a light quantity level for an ordinary image reading operation.
To acquire paper fingerprint data (paper fingerprint information), a conventional method includes setting a small gain adjustment value for an image signal when a reading apparatus reads paper fingerprint information, or decreasing the light quantity of a lamp in an optical unit.
As discussed in Japanese Patent Application Laid-Open No. 07-110641, a document feeder can operate in both a fixed-reading mode and a feeding-reading mode. In the fixed-reading mode, the document feeder stops a document on a document positioning glass plate while an optical reading device moves to read an image on the document. In the feeding-reading mode, the optical reading device performs image reading processing in a stationary state while the document feeder conveys the document.
A machine model, if operable in both the fixed-reading mode and the feeding-reading mode, can flexibly switch its operation mode between the fixed-reading mode and the feeding-reading mode if a user changes the type of a copy mode. After a reading apparatus completes image reading processing according to the fixed-reading mode while moving its optical unit, the reading apparatus returns the optical unit to the home position to start reading an image on the next document. On the other hand, if a reading apparatus performs image reading processing in the feeding-reading mode while conveying a document, document replacement time decreases.
However, the above-described conventional reading method includes nothing about reading of paper fingerprint information. If a reading apparatus reads an image of a document after completing the registration and collation of paper fingerprint information, the reading apparatus performs reading processing for acquiring paper fingerprint data and for acquiring image data independently. Thus, the method cannot realize a high-speed document reading operation.
If a document feeder performs an image reading operation after completing registration and collation of paper fingerprint information, a user is required to set a document twice on a document positioning glass plate. Thus, this process is time consuming.
A conventional document feeder can acquire both paper fingerprint data and image data if the document feeder performs reading processing twice in the fixed-reading mode. However, in this case, the document feeder moves an optical unit twice along a document to perform scanning of the document. Therefore, it takes a long time to complete the reading and document replacement processing.
Furthermore, a conventional document feeder can use a reversing path to read paper fingerprint data and image data from a document in the feeding-reading mode. This method also requires a long time to accomplish document replacement because the document feeder reverses each document in the reversing path.
Moreover, if a document feeder includes another optical sensor dedicated to acquire paper fingerprint information, the cost would increase.